A comparative study of the structure and corrosion resistance of ZnAl hydrotalcite conversion layers at different Al3+/Zn2+ ratios on electrogalvanized steel

T. T. Pham1,2, T. D. Nguyen1, Y. Paint3, M. Gonon2, T. X. H. To1, M.-G. Olivier2,3

1 Institute for Tropical Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam
2 Université de Mons, Materials Science Department, Place du Parc 20, Mons, Belgium
3 Materia Nova, Parc Initialis, Mons, Belgium

E-mail address: thuthuy.pham@umons.ac.be

Hydrotalcites with anion exchange capacity is used as inhibitor container for corrosion protection of metals and alloys 1. Moreover, they can directly grow on a substrate forming a barrier layer with strong adhesion by simple operations, so they stand out from other nanocarriers in corrosion protection 2. In recent years, the mechanisms of hydrotalcites formation and corrosion protection by the HT conversion films on galvanized steel have been started to be investigated 3,4. However, the optimization conditions of the formed HT conversion films on electrogalvanized steels have not yet been fully characterized.

Therefore, the dissimilarities of the composition, crystal structure and corrosion resistance of ZnAl hydrotalcite (ZnAl-HT) conversion films grown “in situ” on electrogalvanized steel substrate (EG steel) were investigated for different Al3+/Zn2+ ratios at pH 12. The corrosion resistance of all conversion films in 0.1 M NaCl was compared through polarization curves and electrochemical impedance spectroscopy (EIS). The polarization curves indicated that the ZnAL-HT films provided anodic inhibition for EG steel substrate and the inhibition efficiency of the ZnAl-HT conversion films increases sharply with decreasing the Al3+/Zn2+ ratios from 5/1 to 5/3, while, for the 5/4 and 5/5 ratios, the corrosion resistance of ZnAl-HT conversion films showed a downward trend after two immersion hours. However, the corrosion resistance of HT conversion films with the Al3+/Zn2+ ratios from 5/3 to 5/5 remained stable for longer immersion time. The dependence of the corrosion resistance on the Al3+/Zn2+ ratios was discussed considering the composition, morphology, structure and thickness of resulting conversion films characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electronic microscopy (SEM) and electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). The corrosion protection of the ZnAl-HT films can be ascribed to the barrier properties, ion-exchange competitive adsorption of chloride ions and protective deposition of ZnO on EG steel surface.

References

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